A semiconductor manufacturing apparatus aligns a substrate prior to processing the substrate (e.g., exposure and injection). As one process for alignment, there is a process called prealignment (coarse alignment). This process is performed to coarsely align (prealign) the substrate so that the positional deviation of the substrate placed on a substrate processing stage falls within a predetermined range before processing the substrate on the substrate processing stage.
For example, in a semiconductor exposure apparatus, the prealignment process can be performed for the purpose of aligning the substrate which is never used in a lithography process (exposure) to determine the position of a pattern to be formed (an underlying pattern used in the next exposure), and prealigning to feed the substrate, which has been used in the lithography process once or more and has a mark for measuring the position of the substrate, to a field of view of a measurement device (e.g., an image processing device) for aligning the substrate at a high precision required in the exposure process.
For example, the following methods are employed in the prealignment process.
(a) A method of aligning the substrate by pushing a plurality of pins against the edge of the substrate (peripheral portion of the substrate) placed on as substrate holder.
(b) A method of, by using a substrate moving mechanism for holding and moving the substrate in a plane direction and a rotational direction, and a measurement device for measuring the position of the edge of the substrate using a linear image sensor, and the like, obtaining the position of the edge of the substrate on the basis of the output result of the measurement device, and moving the substrate by the substrate moving mechanism so that the edge of the substrate is at a predetermined position.
(c) A method of, by using the substrate moving mechanism for holding and moving the substrate in the plane direction and the rotational direction, and the measurement device for measuring the position of the edge of the substrate using the linear image sensor, and the like, calculating the position of the edge of the substrate by the measurement device while rotating the substrate by the substrate moving mechanism, and obtaining the central position and the size of the substrate on the basis of the calculation result, thereby moving the substrate by the substrate moving mechanism on the basis of these pieces of information.
However, an alignment reference for aligning the substrate in the above methods (a) and (b) is different from that in the method (c). That is, in the above methods (a) and (b), the edge of the substrate is aligned to the predetermined position. However, in the method (c), the center of the substrate is aligned to the predetermined position.
Between the substrates respectively aligned by the prealignment apparatus with the different alignment references, the positions of the prealigned substrates placed on the processing stage can be different from each other. If these substrate processing apparatuses with the different alignment references process the same substrate, various problems arise.
Assume that a substrate processing apparatus A incorporates a prealignment apparatus which employs the method (a), and a substrate processing apparatus B incorporates a prealignment apparatus which employs the method (c). The substrate processing apparatus A transfers (exposes) a pattern onto the substrate which is never exposed, and the substrate processing apparatus B processes the substrate in the next process. In this case, the position of a mark on the substrate is different from that expected in the substrate processing apparatus B because the alignment reference of the apparatus A is different from that of the apparatus B.
Therefore, when the substrate processing apparatus B measures the mark position for alignment at a high precision by image processing, and the like, the mark on the substrate may fall outside the measurement field of view. That is, between the apparatuses with the prealignment mechanisms respectively with the different alignment references, a so-called “mix and match” process cannot be implemented, thus posing a problem.
As a measure against this problem, the following methods are considered.
(1) When the mark falls outside the measurement field of view in measuring the mark position for fine alignment (high-precision alignment), the alignment is manually assisted.
(2) Even when the substrate processed by the apparatuses with the different prealignment references is to be processed, the measurement field of view of the measurement device for the fine alignment is enlarged to allow detection of the measurement mark.
(3) When the mark is not observed in the field of view of the measurement device in measuring the mark on the substrate by the measurement device for the fine alignment, the mark is searched (Japanese Patent Laid-Open No. 11-16806).
However, in the methods (1) and (3), the processes require manual assist and search, thereby decreasing the substrate processing throughput of the device per unit time.
In the method (2), the mechanism becomes complicated, the cost of the device increases and the subject processing throughput decreases. More specifically, as a pattern has been further micropatterned recently, a high-precision substrate position detection needed for the measurement device for fine alignment is also required. As a method of implementing a high-precision (i.e., high-resolution) measurement device with a large field of view, for example, there is available a method of measuring the mark position by switching magnifications using a mechanism for switching measurement magnifications. However, in such a method, the mechanism becomes complicated, the cost of the apparatus increases, and the substrate processing throughput per unit time decreases because the low-magnification measurement process, which is not required in the conventional method, is added.